Mineral chemistry constrains on crystallization conditions and petrological evolution of the Teixeira Batholith granitoids, Borborema Province, NE Brazil

Abstract

The Ediacaran Teixeira Batholith comprises an EW - elongated intrusion of c. 800 km2, emplaced in supracrustal rocks and orthogneisses immediately south of the central portion of the Patos Shear Zone, at the limit between the North and Central Subprovinces of the Borborema Province. It is composed of syenogranite, monzogranite and quartz syenite, whose petrographic and textural aspects allow subdivide the batholith into six facies. From petrographic data, mineral chemistry, and zircon trace element composition (LA-Q-ICPMS), the physical crystallization parameters (T, P and fO2) were obtained, as well as important information for granitoids petrogenesis. The mafic mineral assemblage in these granitoids is dominated by amphibole, with Fe/(Fe + Mg) ratio ranging from 0.57 to 0.72 (hastingsite, ferro-ferri-hornblende and ferro-pargasite), in addition to clinopyroxene, mainly of hedenbergite composition and biotite that shows Fe/(Fe + Mg) ratio ranging from 0.4 to 0.7 and are classified as siderophyllite and eastonite. Titanite, epidote, zircon, magnetite, and pyrite are the main accessory phases, and occur with petrographic and chemical features typical of primary origin, constituting a mineral association like that observed in magnetite-series granites. The paragenesis and chemical signature of the studied minerals suggest that the Teixeira Batholith is constituted by oxidized I-type granites. In particular, the Hf contents (9810–11143 ppm) of the studied zircon crystals, together with the biotite composition and the presence of magmatic epidote, suggest that these granitoids were generated from a magma with high-potassium affinity and crystallized at a temperature ranging from 995 to 701 °C and pressure ranging between 4.7 and 3.7 kbar; conditions corresponding to intermediate crustal levels.